During the Greco-Persian War in 490 BCE, Phidippides, a 40-year-old herald messenger (professional running-courier) ran the
26 miles from a battlefield near Marathon, Greece, into Athens carrying momentous news of Greek victory. Upon arriving at
the Acropolis, he proclaimed: ‘Joy, we have won!’ and then immediately collapsed and died.1 Fast-forward about 2500 years to an era when the baby-boomer's came of age and long-distance running boomed. The prevailing
logic held that aerobic exercise is clearly good for one's health and that, if some is good, more must be better. In 1975,
Dr Thomas Bassler, a physician/runner, boldly proclaimed that, if you could run a marathon, you were immune to death from
coronary heart disease (CHD).2 This urban myth has long since been disproven; indeed an emerging body of evidence suggests the opposite: extreme endurance
exercise may exact a toll on cardiovascular (CV) health.

‘Show me the bodies’

After our recent articles on this topic,1,3–5 Amby Burfoot, winner of the 1968 Boston Marathon and Editor-at-Large for Runner's World Magazine, challenged our assertions about the dangers of extreme endurance efforts by demanding, ‘Show me the bodies’. Amby has a
good point: the risk of dropping dead in a marathon is remote, about 0.5 to 1 in 100,000 participants.6 But the occasional marathoner or triathlete who dies while strenuously exercising is the ‘canary in the coal mine’. Chronic
extreme exercise appears to cause excessive ‘wear-and-tear’ on the heart, inducing adverse structural and electrical remodelling,
which offsets some of the CV benefits and longevity improvements conferred by moderate physical activity. Thus, even though
chronic extreme exercise may not kill you, it may erase many of the health advantages of regular moderate exercise.

Indeed, regular vigorous exercise is probably the single best step a person can take to ensure robust CV health. In a …